In general, a bearing requires a sealing function and thus is disposed with a seal assembly equipped with a seal member at a tip end of an opening of a gap formed between an outer ring and an inner ring. The seal assembly comprises a first seal frame press-fitted to the outer ring, a second seal frame firmly press-fitted into the inner ring and a seal member for being inserted into at least one of the first and second seal frames to seal a gap formed between the first and second seal frames.
The seal assembly serves to simultaneously prevent leakage of oil (grease) from within the bearing to the outside and prevent intrusion of water, water steam, dust or the like into a bearing. The seal assembly also serves to maintain lubrication, prevent thermal resistance and support a load, which is the main function of the bearing, thereby enabling a smooth rotation.
However, there is a structural drawback in the seal assembly of the prior art thus described in that it either occupies a lot of space or little space. In other words, in order for a seal assembly to properly perform, there should be an appropriate amount of space occupied by the seal assembly. For instance, a bearing applied to an automobile hub is designated with a boundary condition and a prescribed space of the bearing is occupied by a seal assembly. When an occupied space of the seal assembly is made smaller, the capacity of the bearing can be increased. When the occupied space of the seal assembly is made larger, the function of the seal assembly can be improved, but the capacity of the bearing decreases such that design of the seal assembly has a close relationship not only with the sealing performance of the bearing but also with the capacity of the bearing, in other words, life of the bearing.
Another structural problem is an operational torque of a seal assembly itself. Generally, a seal assembly is formed with lip members made of resilient polymer abutting on a prescribed surface of a bearing or to a prescribed surface comprising the seal assembly for preventing intrusion of foreign objects and for sealing. The contact area of the lip members determines the sealing performance of the seal assembly and operational torque characteristics.
When the contact area (i.e. interference) between the lip members and the contact surface is large, the sealing performance improves but, as a result, the operational torque of the seal assembly itself increases due to excessive contact. The outcome of the increased operational torque results in an early wear and tear and a generation of heat in the lip members, thereby reducing the life of the seal assembly.
Meanwhile, when the interference is small between the lip members and the contact surface, the operational torque may be improved. However, prevention of intrusion of foreign objects and the sealing performance deteriorates, resulting in a poor sealing performance and bringing about an early leakage of oil (grease), intrusion of water or the like, and an early damage to the bearing.
A conventional seal assembly generally includes one or two seal frames and seal members with lips press-fitted into the seal frame. Before a bearing is installed to the seal assembly, the seal assembly itself is separately assembled and then axially disassembled from the bearing. Under this circumstance, a lot of time and cost is consumed prior to installing the bearing to the seal assembly. Once the seal assembly is disassembled, leakage of grease or the like in the seal assembly can be expected, thereby causing difficulty in handling the bearing.